Tomosynthesis, cone beam computed tomography (CBCT) or cone beam CT, and computed tomography (CT) are well known medical imaging methods, helpful for evaluating the condition of internal structures and organs. 3-D imaging of a patient or other subject has been made possible by a number of advancements, including the development of high-speed imaging detectors, such as digital radiography (DR) detectors that enable multiple images to be taken in rapid succession.
Apparatus for tomosynthesis and CBCT are known. Such apparatus include a support structure; a scanner assembly coupled to the support structure, and includes a digital detector to capture an image by the detector; a radiation source; and a control system coupled to the support structure to provide an interface for operation of the apparatus. The detector moves along a detector path, wherein the detector path has a distance that is sufficiently long to allow a scan volume to be positioned within the detector path.
Cone beam computed tomography (CBCT) or cone beam CT technology provides a diagnostic tool for providing 3-D volume images. Cone beam CT systems capture volumetric data sets by using a DR detector and an x-ray source. The source and detector are typically affixed to a gantry that rotates about the object to be imaged. The source directs, from various points along its orbit around the subject, a divergent cone beam of x-rays toward the subject. The CBCT system captures projections throughout the rotation, for example, one 2-D projection image at every degree of rotation. The projections are then used in reconstruction of a 3D volume image using various reconstruction techniques. Among well known methods for reconstructing the 3-D volume image from the 2-D image data are filtered back projection (FBP) approaches. CBCT systems can be particularly useful for imaging legs, arms, and other extremities.
Tomosynthesis, also referred to as digital tomosynthesis, is a method for performing high-resolution limited-angle tomography at radiographic dose levels. Tomosynthesis has been adapted for a variety of clinical applications, including vascular imaging, dental imaging, orthopedic imaging, mammographic imaging, musculoskeletal imaging, and chest imaging. Tomosynthesis combines digital image capture and processing with simple tube/detector motion as used in conventional computed tomography (CT).
However, though similar to CT in some aspects, tomosynthesis has some differences that characterize it as a separate technique. In CT, for example, the source/detector arrangement typically makes at least a complete 180-degree plus fan angle revolution about the subject obtaining a complete set of data from which fully 3-D volume images may be reconstructed. Digital tomosynthesis, on the other hand, uses a limited range of rotation angles (e.g., 15-60 degrees) with a lower number of discrete exposures (e.g., 7-51) than CT, which can obtain hundreds of 2-D projection images. This incomplete set of projections for tomosynthesis is digitally processed to yield images with some of the depth representation of conventional tomography, but having a sharply limited depth of field. Because the image processing is digital, a series of slices at different depths and with different thicknesses can be reconstructed from the same acquisition. However, since fewer tomosynthesis projections are needed than CT to perform the reconstruction, radiation exposure and cost are significantly reduced.
Reconstruction algorithms for tomosynthesis are similar to those used for conventional CT. To handle the computational complexity of these algorithms, a number of manufacturers have produced practical systems using off-the-shelf graphical processing units (GPUs) that can perform full 3-D volume reconstruction in a few seconds.
U.S. Pat. No. 8,233,690 (Ng), incorporated herein in its entirety by reference, describes a dynamic tomographic image reconstruction and rendering on-demand.
U.S. Pat. No. 8,280,135 (McCollough), incorporated herein in its entirety by reference, is directed to a system and method for highly attenuating material artifact reduction in x-ray computed tomography.
Medical practitioners use tomosynthesis in a number of diagnostic applications, such as for a range of extremity imaging functions, where the full 3-D volume of CT is not necessary and where the added complexity of handling metal-related artifacts and other volume imaging artifacts present cost and computational burden that can make accurate diagnosis more difficult. There is a need to provide tomosynthesis representation of volume data even where the full set of CT image data might otherwise be available.